Hypoxia exerts oxidative stress and changes in expression of antioxidant enzyme genes in gills of Mytilus galloprovincialis (Lamarck, 1819)

Bivalve molluscs are widespread in coastal environments, where they are subjected to a wide range of environmental fluctuations, which can represent a significant impact to their antioxidant status. Hypoxia is a global problem affecting the world’s shallow waters, which is forecast to increase in coastal areas due to anthropogenic pressure and global warming. In this work, the effects of 24 h exposure to hypoxia (0.2 mg O2 l−1) on antioxidant parameters of Mytilus galloprovincialis were investigated. Functional parameters of gill samples (the number of dead cells and intracellular reactive oxygen species concentration) were measured by flow cytometry, and the expression level of antioxidant enzyme genes (CAT, GST, SOD) as well as NADH dehydrogenase subunit 2 were analysed using transcriptome analysis. Gills responded to oxygen depletion by an increased total number of intracellular reactive oxygen species, which was accompanied with high levels of mortality of cells (10 times higher compared with control). Significant increases of Mn-superoxide dismutase, glutathione S-transferase and NADH dehydrogenase subunit 2 gene expression levels were observed. Hypoxia did not cause changes in the expression of CAT. The results indicate an overall shift in antioxidant parameters in gill tissue that may represent a certain level of oxidative stress in mussels and decreased capacity of the antioxidant system to maintain redox homeostasis after exposure to hypoxia.